Ensuring Material Performance Meets Design

Underpinning any structural design is the assumption that the material chosen has the structural performance called up in the actual design. As designers, we are commonly asked to span greater distances, carry greater loads in an effort to produce economic designs. An example of this is the specifically designed multi-storey apartment buildings where the axial load capacities of the wall-framing studs are being pushed to their limits. It is in these circumstances where the assumption about the material becomes more and more critical. Client expectations can also be quite demanding and the threat of legal action bought on a structure performing outside the customer’s expectation is very real. In specifically designed structures with obvious, deliberate, and discrete load paths any differences between design properties and supplied properties can reflect negatively on the performance of the structure, as there is no redundancy or ‘load sharing’ ability, which there tends to be for buildings designed under NZS3604. For instance if the timber design uses a Modulus of Elasticity of 10GPa and say the timber supplied has a average MoE of 8.5 GPa then all the calculated deflections could be increased by up to 18%.